Expression of chaA, a sodium ion extrusion system of Escherichia coli, is regulated by osmolarity and pH.

ChaA, one of the sodium ion extrusion systems of Escherichia coli, was found to function at high pH [Biochim. Biophys. Acta 1363 (1998) 231]. A chaA-lacZ transcriptional fusion gene was constructed using chaA of E. coli O157:H7 and its expression was observed in strains derived from E. coli K12. The fusion gene was expressed at high pH and was induced by the addition of NaCl, KCl or sucrose. The amount of chaA mRNA measured by reverse transcription-polymerase chain reaction (RT-PCR) was increased by the addition of sucrose to alkaline growth medium. These results suggested that chaA expression was regulated by medium osmolarity and pH.